60 Auto Fundamentals
to minimize torque defl ections. Small shock
absorbers are sometimes employed, especially
on diesel engines, to further control vibration.
The three-point suspension, used mostly
on rear-wheel drive vehicles, is one of the most
popular. This method uses one mount on either
side of the engine near the front and one at the
back, usually under the transmission. However,
other setups use two-, three-, four-, or fi ve-point
engine mount arrangements. This varies from
each model and manufacturer. Figure 3-26
shows a fi ve-point mounting pattern.
Other Engine Designs
Although most automobiles and light trucks
use four-stroke, reciprocating, gasoline engines,
there are a number of other engine types used
in late-model vehicles. Some of these engines
burn a fuel other than gasoline. Others are vari-
ations of the conventional four-cycle engine. A
few of the more common alternative engines are
detailed in the following sections.
Two-Stroke and Four-Stroke Cycle
Diesel Engines
A two-stroke cycle diesel engine is some-
what different than the two-stroke gasoline
engine discussed earlier in this chapter. The two-
stroke cycle diesel engine utilizes an exhaust
valve. No fuel mixture enters the crankcase.
Due to the pressures involved, a supercharger is
used to force air into the cylinder intake ports.
Figure 3-27 shows the two-stroke cycle opera-
tion in a diesel engine. Notice that air rushing in
through the cylinder liner ports helps scavenge
the cylinder by fl owing out the exhaust passage
for a portion of the piston travel. Since only air
enters the cylinder, there is no loss of fuel.
Figure 3-28 shows a typical four-stroke
cycle, four-cylinder automotive diesel engine.
Inline fi ve-, six-, and V-8 diesels are also used,
Figure 3-29. Diesel fuel injection system opera-
tion is discussed in Chapter 10, Fuel Injection
Systems.
Rotary Engines
The rotary engine was used on a few vehi-
cles for many years and was not produced in
large numbers. The rotary engine is very power-
ful for its size. This engine is often referred to as
a Wankel engine.
The rotary engine has fewer moving parts
than a piston engine. Since it has no recipro-
cating motion, the rotary engine produces less
vibration and offers more horsepower. Draw-
backs of the rotary engine included difficulty
meeting emission control standards, and poor
fuel economy compared to a piston engine of
similar power output.
Rubber
Fluid
Orifice
Diaphragm
Air chamber
Movable
plate
Right
mount
Center
mount
Front
mount
Rear mount
Left mount
Figure 3-26.
One type of front-wheel drive engine mount. The fl uid sealed in the mount absorbs low speed vibrations.
Toyota